The present invention relates generally to temperature control systems for multi-compartment refrigerators, and more particularly to evaporator fan and damper control systems for regulating the temperature of the fresh food and freezer compartments of a refrigerator.
In a typical multi-compartment refrigerator there are several methods for controlling the temperature of each of the compartments. It is common practice for the refrigeration system, i.e. the compressor, evaporator, fan, etc., to directly cool the freezer compartment. Air from the freezer compartment is directed to the fresh food compartment by means of an opening from the freezer to the fresh food compartment. Air is throttled in this opening by means of some type of air damper control. The damper has traditionally been a manually operated mechanism, which can be adjusted by the user to vary the freezer temperature. The fresh food temperature is generally controlled by a thermostat which senses the fresh food compartment temperature. The thermostat governs the operation of the compressor and evaporator fan. The resulting freezer temperature is a function of the fresh food compartment set point temperature and the position of the manual damper. It is generally known that this type of control system is not ideal for temperature stability of the freezer, especially when the outside temperature changes and the fresh food set point temperature is changed. The advantage of this system is that it is very inexpensive to produce.
A less traditional means of control used currently in only approximately 15% of standard refrigerators produced in the United States is to cycle the compressor using a thermostat that senses the freezer temperature. The air flow to the fresh food compartment is attenuated by a modulating air damper control. This control uses a refrigerant charged bellows that expands and contracts in response to the temperature of the fresh food compartment. The bellows movement is then used to drive a door, located in the air flow stream, to attenuate air flow to the fresh food compartment. The movement of the door is very predictable, thus allowing this device to be offered on a production basis. This type of control system allows for more accurate temperature control for both compartments than the method described above. Outside temperature variance and door openings are better compensated using this system.
The principal drawback for such a system is cost. Manufacturers positioning certain product as xe2x80x9chigh performancexe2x80x9d are the users of this type of system. The second drawback for such a system is that the fresh food compartment is still slaved to the freezer compartment. The modulating damper can better compensate for changes in set point temperature of the freezer than a manually operated device, but some changes to the temperature of the fresh food compartment are apparent since the fan is only operating when the compressor is operating. The compressor operation is dependent on the thermostat, which is sensing freezer temperature only. Another advantage of the modulating damper is that no external power is required for it to perform. Refrigerator manufacturers are very concerned about power consumption, and are very competitive in reducing power consumption. They are also under tremendous pressure from the Department of Energy to make incremental power consumption reductions.
In response to these pressures and desires to reduce power consumption, manufacturers have sought to solve the problem of temperature variances due to the slaving of the air flow from the freezer to the fresh food compartment. Systems resulting from such endeavors, unlike the prior systems that operated based only on the temperature input from one of the freezer or the fresh food compartment, control the refrigeration components by sensing both the freezer temperature and the fresh food compartment temperature and by using a plurality of single and multi-throw switches to transfer control between the two thermostats. Unfortunately, the use of so many single and multi-throw switches to coordinate the control of the two thermostats, the evaporator fan, and the damper motor greatly increases the cost and complexity of such a system. The required wiring of these switches also increases the labor cost and reduces the overall reliability of such a system.
Such systems, such as that illustrated in FIG. 3, typically utilize a freezer thermostat 101 to control the compressor 103, condenser fan 105, and evaporator fan 107 to regulate the freezer temperature to the set point of the freezer thermostat. A multi-contact fresh food compartment thermostat 109 is then used to control a motorized damper 111 that regulates an opening between the freezer and the fresh food compartment. In addition to the damper, the motor 111 also operates a multi-control-surface cam used to control two multithrow switches 113, 115 that connect and disconnect control of evaporator fan 107 between the two thermostats 101, 109 and energize the motorized damper 111 to open or close.
The state of the switches illustrated in FIG. 3 relates to both compartments being at or below their set point temperatures. If the fresh food compartment thermostat 109 calls for cool (connection between terminal A and B), the motorized damper 111 is energized to open the damper and rotate the cam. When the cam reaches its fully open position, both switches 113 and 115 transition. Switch 113 then allows the fresh food compartment thermostat 109 to control the evaporator fan 107. This increases circulation between the compartments, thereby reducing the amount of time that it takes to achieve the desired temperature. The cam control surface that transitions the evaporator control switch 113 waits until the damper is fully open to allow the fresh food thermostat 109 to energize the fan 107 to reduce the power consumption of running the fan while the damper is in transition. In this state, however, the control of the evaporator fan via the freezer thermostat is disabled as its input through the multi-throw switch 113 is opened.
When the fresh food compartment reaches its desired temperature, the multi-contact fresh food compartment thermostat 109 switches to again close contacts A and C. The motorized damper 111 is energized to drive the damper closed. The control surface on the cam immediately transitions switch 113 to return control of the evaporator fan 107 to the freezer thermostat 101. However, since the control cam does not transition the switch 115 until the damper is fully closed, a power failure that occurs while the damper is in the process of closing but is not yet fully closed can result in a condition where the damper cannot be opened and the evaporator fan 107 cannot be energized. This situation occurs when the power failure lasts long enough for the fresh food compartment to warm above its thermostat set point, thereby closing contact A and B of thermostat 109. Since the switch 115 has not been transitioned by the cam to the state show in FIG. 3 because the damper was not allowed to fully close, no power is provided to the motor 111. As such, the switch 113 stays in the freezer control position illustrated in FIG. 3, which means that the call for cooling from the fresh food compartment cannot be accommodated, and the temperature in this compartment. will likely continue to rise. A service call is then required to reset the cam and the control switches to allow the system to work properly again.
One system that overcomes this failure condition is described in U.S. Pat. No. 5,490,395, entitled AIR BAFFLE FOR A REFRIGERATOR. In the system of this patent, the functionality of the single motorized damper control switch 115 illustrated in FIG. 3 is divided among two single pole, single throw switches 117, 118 as illustrated in the simplified FIG. 4. Unfortunately, the addition of an additional switch also requires a more complex cam that includes an additional cam control surface and an additional cam control surface follower to actuate the additional switch. While overcoming the problem discussed above, the additional cost and complexity of this solution accompanied with the resulting reduction in overall system reliability makes such a system undesirable and cost ineffective.
Therefore, there continues to exist a need in the art for a system that provides better temperature stability of both the freezer compartment and the fresh food compartment of a refrigerator, while reducing the cost and power consumption and increasing the overall reliability of the system.
In light of the above, the present invention provide a new and improved evaporator fan control system for a multi-compartment refrigerator. More specifically, the present invention provides a new and improved evaporator fan control system that enables coordination between the fresh food compartment need for cooling and the freezer compartment need for cooling, while taking into consideration the operational system requirements for energy efficient defrost control.
In a preferred embodiment of the present invention, an evaporator fan control system is presented that is particularly adapted for a multi-compartment refrigerator having a damper controlling an opening between compartments to allow cooling from a first compartment to be transferred to a second compartment. This system comprises a first thermostat positioned to sense temperature in the first compartment, a second thermostat positioned to sense temperature in the second compartment, and an adaptive defrost timer control module that is operably coupled to the first and the second thermostat to determine when each compartment requires cooling. The adaptive defrost timer control module provides an energization output to an evaporator fan. Preferably, the adaptive defrost timer control module energizes the evaporator fan when the second thermostat indicates that the second compartment requires cooling.
Preferably, the adaptive defrost timer control module also energizes the evaporator fan when the first thermostat indicates that the first compartment requires cooling. In one embodiment the adaptive defrost timer control module prevents energization of the evaporator fan when the adaptive defrost timer control enters a defrost cycle, regardless of a status of the first and the second thermostats. In an embodiment where the multi-compartment refrigerator includes a damper that controls a flow of air between the first and the second compartments and that opens when the second thermostat indicates that the second compartment requires cooling, the adaptive defrost timer control module further includes a time delay between indication from the second thermostat that the second compartment requires cooling and energization of the evaporator fan. The time delay is of a duration sufficient to allow the damper to open. However, in one embodiment the time delay does not operate when the second thermostat indicates that the second compartment no longer requires cooling, thereby allowing the adaptive defrost timer control to immediately de-energize the evaporator fan.
In an alternate embodiment of the present invention, an evaporator fan control system for a refrigerator having a freezer compartment and a fresh food compartment is presented. The cooling of the fresh food compartment is controlled via a damper regulating an opening between the freezer compartment and the fresh food compartment. The system comprises an adaptive defrost timer control module having an output coupled to the evaporator fan for turning the evaporator fan on and off, and a thermostat positioned to sense a temperature of the fresh food compartment. The thermostat provides an input to the adaptive defrost timer control module indicating when the fresh food compartment requires cooling. Further, the adaptive defrost timer control module turns the evaporator fan on when the thermostat indicates that the fresh food compartment requires cooling.
Preferably, the adaptive defrost timer control module turns the evaporator fan off when in a defrost cycle regardless of an indication from the thermostat that the fresh food compartment requires cooling. In one embodiment, the system further comprises a second thermostat positioned to sense a temperature of the freezer compartment. This second thermostat provides an input to the adaptive defrost timer control module indicating when the freezer compartment requires cooling. The adaptive defrost timer control module turns the evaporator fan on when the second thermostat indicates that the freezer compartment requires cooling. Preferably, the adaptive defrost timer control module turns the evaporator fan off when in the defrost cycle regardless of an indication from the second thermostat that the freezer compartment requires cooling. Further, the adaptive defrost timer control module turns the evaporator fan off when neither the thermostat indicates that the fresh food compartment requires cooling, nor the second thermostat indicates that the freezer compartment requires cooling.
Further, the adaptive defrost timer control module delays turning the evaporator fan on for a period of time after the thermostat indicates that the fresh food compartment requires cooling to allow the damper to open between the freezer and the fresh food compartment. However, the adaptive defrost timer control module does not delay turning the evaporator fan off after the thermostat indicates that the fresh food compartment no longer requires cooling.
In yet a further embodiment of the present invention, an evaporator fan control system for use in a frost free multi-compartment refrigerator is presented. The refrigerator has a freezer compartment that is cooled by a compressor and an evaporator fan, and a fresh food compartment that is cooled by operation of the evaporator fan to blow air from the freezer compartment into the fresh food compartment through a damper controlled opening between the two compartments. Each compartment has installed therein a thermostat. The refrigerator further includes a defrost heater to effectuate frost free operation. The system of this embodiment comprises an adaptive defrost timer control module having control inputs for sensing the thermostat in the fresh food compartment and the thermostat in the freezer compartment, and control outputs for energizing the evaporator fan, the compressor, and the defrost heater in accordance with programmed logic. This programmed logic is contained within the adaptive defrost timer control and includes a logical OR gate having an input indicating that the thermostat installed in the fresh food compartment requires cooling and an input indicating that the thermostat installed in the freezer compartment requires cooling and an output. The logic also includes a logical NAND gate having an input from the output of the logical OR gate and an inverted input indicating that the refrigerator is in a defrost cycle and an output. The adaptive defrost timer control module energizes the evaporator fan upon generation of a logical 1 at the output of the logical NAND gate.
Preferably, the programmed logic includes a time delay on the input of the logical OR gate indicating that the thermostat installed in the fresh food compartment requires cooling. This time delay is of a period sufficient to allow the damper to open. Further, the time delay does not operate when the input of the logical OR gate indicates that the thermostat installed in the fresh food compartment no longer requires cooling.